Magnetoresistive sensor having improved antiparallel tab free layer biasing

ABSTRACT

A magnetoresistive sensor having improved free layer biasing and track width control.

FIELD OF THE INVENTION

The present invention relates to a spin valve read head stabilizedwithout hard bias layers and, more particularly to an antiparallelcoupled (AP) tab design for improved free layer stabilization and trackwidth control.

BACKGROUND OF THE INVENTION

The heart of a computer is an assembly that is referred to as a magneticdisk drive. The magnetic disk drive includes a rotating magnetic disk,write and read heads that are suspended by a suspension arm adjacent toa surface of a rotating magnetic disk and an actuator that swings thesuspension arm to place the read and write heads over selected circulartracks on the rotating disk. The read and write heads are directlylocated on a slider that has an air bearing surface (ABS). Thesuspension arm biases the slider into contact with the surface of thedisk when the disk is not rotating but, when the disk rotates, air isswirled by the rotating disk. When the slider rides on the air bearing,the write and read heads are employed for writing magnetic impressionsto and reading magnetic impressions from the rotating disk. The read andwrite heads are connected to processing circuitry that operatesaccording to a computer program to implement the writing and readingfunctions.

The write head includes a coil layer embedded in first, second and thirdinsulation layers (insulation stack), the insulation stack beingsandwiched between first and second pole piece layers. A gap is formedbetween the first and second pole piece layers by a gap layer at an airbearing surface (ABS) of the write head and the pole piece layers areconnected at a back gap. Current conducted to the coil layer induces amagnetic field in the pole pieces which causes flux across the gap atthe ABS for the purpose of writing the aforementioned magneticimpressions in tracks on moving media, such as in circular tracks on theaforementioned rotating disk.

In recent read head designs a spin valve sensor has been employed forsensing magnetic fields from the rotating magnetic disk. The sensorincludes a nonmagnetic conductive layer, hereinafter referred to as aspacer layer, sandwiched between first and second ferromagnetic layers,hereinafter referred to as a pinned layer and a free layer. First andsecond leads are connected to the spin valve sensor for conducting asense current therethrough. The magnetization of the pinned layer ispinned perpendicular to the air bearing surface (ABS) and the magneticmoment of the free layer is located parallel to the ABS, but free torotate in response to external magnetic fields. The magnetization of thepinned layer is typically pinned by exchange coupling with anantiferromagnetic layer.

The thickness of the spacer layer is chosen to be less than the meanfree path of conduction electrons through the sensor. With thisarrangement, a portion of the conduction electrons is scattered by theinterfaces of the spacer layer with each of the pinned and free layers.When the magnetizations of the pinned and free layers are parallel withrespect to one another, scattering is minimal and when themagnetizations of the pinned and free layer are antiparallel, scatteringis maximized. Changes in scattering alter the resistance of the spinvalve sensor in proportion to cos θ, where θ is the angle between themagnetizations of the pinned and free layers. In a read mode theresistance of the spin valve sensor changes proportionally to themagnitudes of the magnetic fields from the rotating disk. When a sensecurrent is conducted through the spin valve sensor, resistance changescause potential changes that are detected and processed as playbacksignals.

A spin valve sensor is characterized by a magnetiresistive (MR)coefficient that is substantially higher than the MR coefficient of ananisotropic magnetoresistive (AMR) sensor. For this reason a spin valvesensor is sometimes referred to as a giant magnetoresistive (GMR)sensor. When a spin valve sensor employs a single pinned layer it isreferred to as a simple spin valve. When a spin valve employs anantiparallel (AP) pinned layer it is referred to as an AP pinned spinvalve. A spin valve is also known as a top or bottom spin valvedepending upon whether the pinning layer is at the top (formed after thefree layer) or at the bottom (before the free layer). A pinning layer ina bottom spin valve is typically made of platinum manganese (PtMn). Thespin valve sensor is located between first and second nonmagneticelectrically insulating read gap layers and the first and second readgap layers are located between ferromagnetic first and second shieldlayers. In a merged magnetic head a single ferromagnetic layer functionsas the second shield layer of the read head and as the first pole piecelayer of the write head. In a piggyback head the second shield layer andthe first pole piece layer are separate layers.

It is important that the free layer of the spin valve sensor bemagnetically stable. During a typical construction of a spin valvesensor a bilayer photoresist is formed on top of multiple full filmsensor layers. These full film layers are then ion milled to form thespin valve sensor with first and second side edges that are typicallytapered at an angle with respect to a normal to the planes of thelayers. First and second hard bias layers and first and second leadlayers are then deposited with the bilayer photoresist still in placeforming what is known in the art as contiguous junctions of the hardbias and lead layers with the first and second side edges of the spinvalve sensor. Magnetostatic fields from the first and second hard biaslayers are employed for the purpose of aligning the magnetic moments ofthe free layer so that they are all in the same direction in a singledomain state. Without the hard bias layers the free layer would be in amulti-domain state with the magnetic domains being defined by numerouswalls. The narrower the track width the greater the magnetic instabilityof the free layer. When the free layer is subjected to applied magneticfields from the rotating disk the domain walls move around which createsmagnetic noise that is superimposed upon the read signal.

The aforementioned process of making contiguous junctions inherentlyresults in a taper of the first and second side edges of the layers ofthe sensor. Unfortunately, the greater the angle or taper of the firstand second side edges of the spin valve sensor the less theeffectiveness of first and second hard bias layers. When the first andsecond side edges of the spin valve sensor are tapered the first andsecond hard bias layers take on the soft magnetic properties of the freelayer causing the first and second hard bias layers to be magneticallysofter and less capable of applying a magnetostatic coupling forstabilizing the free layer. The first and second hard bias layers are attheir maximum effectiveness when the first and second side edges of thespin valve sensor are vertical sensor are vertical or parallel to anormal to the planes of the layers. This vertical configuration has notbeen obtainable with the bialayer photoresist and ion milling steps forforming the first and second side edges of the spin valve sensor.Accordingly, there is a strong-felt need for a biasing scheme tolongitudinally bias the free layer into a single domain state when thefirst and second side edges of the spin valve sensor are tapered.

Pursuant to the above objective, attempts have been made to bias thefree layer of a spin valve using antiparallel pinned tabs at side edgesof the spin valve outside of the active area of the sensor. Such designsemploy first and second first ferromagnetic layers formed outside of theactive area of the sensor and separated by a nonmagnetic spacer layer.One of the layers is exchange coupled with an antiferromagnetic layer,very strongly pinning these ferromagnetic layers outside of the activearea of the sensor. One of the ferromagnetic layers could be eitherexchange coupled with or contiguous with the free layer so as tostrongly bias the free layer.

However, such designs have experienced challenges in stabilizing thefree layer while precisely defining the track width of the sensor. Asone skilled in the art may appreciate, the strong biasing that can beachieved at the outer edges of the free layer can essentially pin theouter edges of the free layer in the active area of the sensor. Thispinning can decrease toward the center of the sensor leading tonon-uniform biasing, and therefore, poorly defined track width.

Therefore, there remains a strong felt need for a mechanism for robustlystabilizing the free layer of a magnetoresistive sensor while preciselydefining the track width of the sensor and allowing sufficient, uniformfree layer sensitivity.

SUMMARY OF THE INVENTION

The present invention provides a magnetoresistive sensor having improvedfree layer stability and track width control. A ferromagnetic pinnedlayer has first and second sides that are disposed outside of an activeregion of the sensor. A ferromagnetic layer that is magnetostaticallycoupled with at least a portion of the free layer extends beyond thelateral side walls of the pinned and free layers and exchange coupleswith the antiferromangetic material.

The sensor can be considered to have a center or active region, definedby the track width of the sensor. First and second intermediate regionscan be considered to extend from the out edge of the active region tothe lateral side walls of the pinned and free layers. First and secondouter regions can be considered to extend laterally outward from theouter edges of the intermediate regions.

The ferromagnetic material that exchange couples with the free layercould be a layer of a synthetic free layer (ie. an antiparallel coupledfree layer) or could be separate bias layers magnetostatically coupledwith the free layer in the intermediate regions.

The present invention advantageously provides pinning of an antiparallelcoupled bias layer, where the pinning occurs some distance from theactive area of the sensor. The magnetostatic coupling of the bias layerwith the free layer occurs mostly outside of the active region, beingdiminished or eliminated within the active region. In this way magneticstability is provided to the free layer that is essentially constantacross the lateral width of the free layer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of thisinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a schematic illustration of a disk drive system in which theinvention might be embodied;

FIG. 2 is an ABS view of a magnetoresistive sensor according to anembodiment of the present invention;

FIGS. 3-6 are ABS view illustrations of the magnetoresistive the sensorof FIG. 2 shown in intermediate stages of manufacture.

FIG. 7 is an ABS view of a magnetoresistive sensor according to anotherembodiment of the invention;

FIG. 8 is an ABS view of the magnetoresistive sensor of FIG. 7 shown inan intermediate stage of manufacture;

FIG. 9 is an ABS view of a magnetoresistive sensor according to yetanother embodiment of the invention in an intermediate stage ofmanufacture; and

FIG. 10 is an ABS view of a magnetoresistive sensor according to stillanother embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best embodiment presently contemplatedfor carrying out this invention. This description is made for thepurpose of illustrating the general principles of this invention and isnot meant to limit the inventive concepts claimed herein.

Referring now to FIG. 1, there is shown a disk drive 100 embodying thisinvention. As shown in FIG. 1, at least one rotatable magnetic disk 112is supported on a spindle 114 and rotated by a disk drive motor 118. Themagnetic recording on each disk is in the form of annular patterns ofconcentric data tracks (not shown) on the magnetic disk 112.

At least one slider 113 is positioned near the magnetic disk 112, eachslider 113 supporting one or more magnetic head assemblies 121. As themagnetic disk rotates, slider 113 is moved radially in and out over thedisk surface 122 so that the magnetic head assembly 121 may accessdifferent tracks of the magnetic disk where desired data are written.Each slider 113 is attached to an actuator arm 119 by way of asuspension 115. The suspension 115 provides a slight spring force whichbiases slider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator means 127. The actuator means 127 as shown inFIG. 1 may be a voice coil motor (VCM). The VCM comprises a coil movablewithin a fixed magnetic field, the direction and speed of the coilmovements being controlled by the motor current signals supplied bycontroller 129.

During operation of the disk storage system, the rotation of themagnetic disk 112 generates an air bearing between the slider 113 andthe disk surface 122 which exerts an upward force or lift on the slider.The air bearing thus counter-balances the slight spring force ofsuspension 115 and supports slider 113 off and slightly above the disksurface by a small, substantially constant spacing during normaloperation.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 129, such asaccess control signals and internal clock signals. Typically, thecontrol unit 129 comprises logic control circuits, storage means and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123 and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position slider 113 to the desired data track on disk112. Write and read signals are communicated to and from write and readheads 121 by way of recording channel 125.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 1 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuators, and each actuator may support anumber of sliders.

With reference now to FIG. 2, a magnetoresistive sensor according to anembodiment of the present has improved track width definition and freelayer stabilization. The sensor 200 includes a pinned layer 202 thatextends substantially beyond a track width TW of the sensor, terminatingin laterally opposed first and second sides 204, 206. The pinned layer202 preferably extends beyond the track width TW a distance of a leastone half the track width TW. First and second layers ofantiferromagnetic material 205, 207, such as for example PtMn abut thesides 204, 206 of the sensor and extend laterally therefrom. The pinnedlayer 202 can be an antiparallel pinned (AP Pinned) layer includingfirst and second ferromagnetic layers 208, 210 separated by a thin,non-magnetic coupling layer 209 such as Ru. The first and secondferromagnetic layers 208, 210 can be constructed of for example NiFe orCoFe. The pinned layer 202 can be pinned by exchange coupling one of theferromagnetic layers 208, 210 with a third layer of antiferromagneticmaterial (AFM) 212 formed thereunder, The sensor may include one or moreseed layers 213 formed under the AFM 212 to assist with achieve properepitaxial crystal structure of the AFM 212.

The sensor 200 also includes a free layer 214, separated from the pinnedlayer by a non-magnetic, electrically conductive spacer layer 216. Thoseskilled in the art will recognize that the present invention could alsobe practiced with a tunnel valve, rather than a spin valve, in whichcase the spacer layer 216 would be a thin non-magnetic, electricallyinsulating layer such as Al₂O₃.

The free layer 214 is a synthetic free layer having first and secondferromagnetic layers 218, 220 separated by a second non-magneticcoupling layer 222 such as Ru. The two ferromagnetic layers 218, 220 ofthe free layer 214 are antiparallel coupled, which improves stability ofthe free layer. A benefit of the present invention is that a portion ofthe second ferromagnetic layer 220 serves as a biasing layer for thefirst ferromagnetic layer 218 as will be described herein below.

With continued reference to FIG. 2, a portion of the secondferromagnetic layer 220 of the free layer 214 extends significantlybeyond the lateral sides 204, 206 of the pinned layer 202. That portionof the second ferromagnetic layer 220 of the free layer 214 is exchangecoupled with the first and second antiferromagnetic layers 205, 207. Itshould be appreciated that this exchange coupling occurs only in theareas where the free layer 214 contacts the first and secondantiferromagnetic materials 205, 207 which is significantly outside ofthe track width region TW of the sensor. This is advantageous, becausethe second layer 220, of the free layer 214 is strongly pinned in theregions where it is exchange coupled with the antiferromagnetic materiallayers 205, 207. This pinning does not stop instantaneously at the pointwhere the exchange coupling stops, but rather tapers off gradually.Therefore, if the exchange coupling were extended to the outer edge ofthe track width TW (ie. to the edge of the active portion of thesensor), the magnetizations of the outer potions of the free layer inthe active area would be excessively stiff and the sensor would sufferfrom insensitivity and non-uniformity of free layer biasing as theeffects of the exchange coupling tapered off. This problem becomes evenmore pronounced as track widths are decreased, as necessitated by everincreasing data capacity requirements.

With continued reference to FIG. 2, the second ferromagnetic layer 220of the free layer 214 is considerably thicker in the regions outside theactive area TW than it is within the active area. In fact the secondlayer 220 of the free layer 214 is preferably at least 15 percentthicker than layer 218 outside the active area than it is within thetrack active area. More preferably, the second layer 220 of the freelayer 214 is about 20 percent thicker in the outer regions than inwithin the active area. The thicker second layer 220 of the free layer214 in the outer regions increases the biasing of the free layer 214 inthe outer regions, but decreases the biasing within the active area soas to allow the magnetization of the free layer within the active areato remain free and capable of rotating in the presence of a magneticfield. This construction provides the perfect balance of magneticstability and free layer sensitivity. The thicker portions 224 of thefree layer 214 can be formed by refill processes that will be discussedin greater detail herein below.

The sensor 200 also includes first and second leads 226, 228, whichterminate at the outer regions of the active area and extend laterallyoutward there from. In fact, the leads 226, 228 advantageously definethe track width TW of the sensor. Sense current will flow to the sensorthrough the leads 226, 228 and will pass through the outer portions 224of the free layer 214 before conducting through the active area of thesensor within the active area of the sensor 200, thereby defining thetrack width TW. Since the magnetoresistive senor 200 allows detection ofa magnetic field by measurement of the electrical resistance through thesensor 200, it is only this active area between the termination of theleads 226, 228 that will contribute to that resistance. As discussedabove this advantageously keeps the pinned portion of the free layer 214sufficiently outside of the active area of the sensor TW to allowsubstantially constant biasing of the free layer 214 in the active areaof the sensor. A capping layer 229, such as Ta, can be provided in theactive area of the sensor 200 between the leads 226, 228 to protect andprevent corrosion of the free layer 214.

With reference now to FIGS. 3-7, a possible method for constructing theabove described sensor will be illustrated. With particular reference toFIG. 3, the third AFM layer 212, pinned layer 202, Cu spacer layer 216,free layer 214, and a Ta capping layer 229 are formed by methods thatinclude, depositing the layers all as full film materials and thenmasking (not shown) and performing a material removal process (notshown) to form the sides 204, 206. Thereafter, the first and secondantiferromagnetic (AFM) material layers 205, 207 are deposited. A CMPprocess may optionally be performed to form a planar upper surface. Aphotoresist mask 302 is then formed using photolithographic processesfamiliar to those skilled in the art, and is formed of a width togenerally coincide with the track width TW of the sensor 200. The photoresist mask 302 can be a bilayer photoresist as shown or could be asimple single layer photoresist mask. With reference to FIG. 4, areactive Ion Etching process (RIE) can then be performed, such as in aCHF₃ atmosphere, to remove the portions of the Ta that are not protectedby the photoresist mask 302.

With reference to FIG. 5, another material removal process, such assputter etching can be used to remove a portion of the secondferromagnetic layer 220. With reference to FIG. 6, ferromagnetic refillmaterial 602 is deposited, preferably of the same material as thatmaking up the previously deposited portion of the second ferromagneticlayer 220 of the free layer, such as NiFe or CoFe. Thereafter the leads226, 228 can be deposited, such as by electroplating and or sputtering.It will then be an easy matter to remove the photoresist layer 302,resulting in the sensor 200 described with reference to FIG. 2. Itshould be noted that the processes described above advantageously leavethe active portions of the free layer protected and completelyunaffected by subsequent process steps such as RIE or sputter etchingprocesses.

With reference now to FIG. 7, a sensor 700 according to anotherembodiment of the present invention employs a single free layer 702. Thesensor 700 has first and second bias layers 706, 708 disposed withinfirst and second intermediate regions 710, 712 that extend from theouter edges of an active region 704 to laterally opposed side walls 714,716. First and second leads 226, 228 define the outer edges of the trackwidth TW, and of the active area 704, by freely conducting sense currentto the outer edges of the active area 704.

The sensor also in includes a pinned layer 202, and a spacer layer 216which extend substantially beyond the active region of the sensorterminating at the first and second laterally opposed sides 714, 716.First and second antiferromagnetic material layers 205, 207 residewithin first and second outer regions 723, 725 abutting the sides 714,716 of the pinned and free layers 202, 702 and extending laterallyoutward there from. The antiferromagnetic layers 205, 207 are exchangecoupled with third and fourth bias layers 724, 726 formed there over.The third and fourth bias layers 724, 726 have inner termination pointsdisposed within the first and second intermediate regions, andsubstantially distant from the center or active region 704, and extendlaterally outward therefrom. These third and fourth bias layers 724, 726are exchange coupled with the first and second bias layers 706, 708. Alayer of non-magnetic material 728 can be provided in the active region704, and would be coplanar with and continguous with the first andsecond bias layers 706, 708. This non-magnetic layer can be formed of amaterial that is similar to that of the first and second bias layers706, 708 except that it has been oxidized to render it non-magnetic andelectrically non-conductive. A process for achieving this will bedescribed herein below. Optionally this portion 728 could be completelyremoved rather than oxidized as will also be described below.

With reference still to FIG. 7, the exchange coupling of theantiferromagnetic layers 205, 207 with the third and fourth bias layers724, 726 in first and second outer regions 723, 725 strongly fixes themagnetization of the bias layers 724, 726. These third and fourth biaslayers 724, 726 are exchange coupled with at least a portion of thefirst and second bias layers 706, 708, and therefore magnetize thesebias layers 706, 708 as well. The first and second bias layers 706, 708antiferromagnetically couple with the free layer 702 in a directionantiparallel with the magnetization of the bias layers 706,708. Thisantiparallel coupling is caused by magnetostatic coupling across thecoupling layer 729 formed between the free layer 702 and the bias layers706, 708. The coupling layer 729 could be for example Ru. A cappinglayer, 730, can be provided between the leads 226, 228.

With reference to FIG. 8, in order to construct a sensor 700, accordingto the embodiment described above, first the AFM 212 pinned layer 202,free layer 702 and spacer layer 216 are formed. Then, the Ru couplinglayer 729 layer and a magnetic layer 802 are deposited on top of thefree layer. The third and fourth bias layers 726, 224 can then be formedby a photolithographic process employing a photoresist mask (not shown).There after the leads can be formed also by a photolithographic processusing a smaller mask (also not shown). After the mask used to form theleads 226, 228 has been removed, a RIE process can be used to removeferromagnetic material, using the leads as a mask to only remove theportions of the ferromagnetic layer 802 in the active region 704. Thisadvantageously, eliminates the magnetostatic coupling in the activeregion leaving the first and second bias layers 706, 708 tomagnetostatically couple with the free layer only in the inactiveintermediate regions 710, 712.

With reference now to FIG. 9, a method for constructing anotherembodiment described above is illustrated. The AFM 212 pinned 202,spacer 216, free 702, hard bias 802 and leads 226, 228 are formed asdescribed above. First the Ta cap layer 730 is removed by the RIEprocess, then, the sensor 700 is exposed to an atmosphere 902 that willoxidize exposed portions of the ferromagnetic layer 802. Such anatmosphere could be for example, water vapor, oxygen or air. This willoxidize only the exposed portion of the ferromagnetic layer that existsin the desired active area of the sensor. The oxidation of theferromagnetic material in the active area of the sensor renders thatportion of the ferromagnetic material non-magnetic and electricallynon-conductive. A preferred material for use as a ferromagnetic materialcould be CoFe which oxidizes readily, or could be CoNiFe, or NiFe.

With reference now to FIG. 10, yet another embodiment of the inventionis described. The sensor 1000 includes a pinned layer 202, and a spacerlayer 216 as before. The sensor 1000 also includes a free layer 1004having a non magnetic coupling layer 1005 formed there over.Ferromagnetic bias layers 1006, 1008 are formed over the free layer 1004in intermediate regions 1010, 1012. The sensor also includes an activeregion 1014, and first and second outer portions 1016, 1018. The pinned,spacer, free, coupling, and bias layers 202, 216, 1002, 1004, 1006, 1008form first and second side walls 1020, 1022 at the juncture between theintermediate 1010, 1012 and outer portions 1016, 1018. Optionally, firstand second layers of electrically conductive lead material 1024, 1026can be formed to abut the first and second side walls 1020, 1022, andextend laterally there from. Such lead layers 2024, 2026 wouldpreferably have an upper surface that is coplanar with an upper surfaceof the bias layers 1006, 1008.

With continued reference to FIG. 10, a non-magnetic, electricallynon-conducting material layer 2028 is formed between the bias layers1006, 1008, and is coplanar therewith. The non-magnetic electricallynon-conducting layer can be deposited along with the bias layers 1006,1008 as a single material layer and then oxidized in a manner similar tothat described with reference to FIGS. 7 and 9.

First and second antiferromagnetic material layers 1030, 1032 are thenformed over the bias layers 1006, 1008 and leads 2024, 2026. Theantiferromagnetic material layers 2030, 2032 are formed withterminations in the intermediate regions, some distance from the activearea, and extend laterally there from. Third and fourth lead layers1034, 1036, preferably formed of Rh, can be provided between thetermination of the ferromagnetic layers 1030, 1032 and the active area1014 of the sensor. In addition, fifth and sixth lead layers 1038, 1040can also be provided over the antiferromagnetic layers 1030, 1032 toprovide additional sense current conduction to the sensor. Those skilledin the art will appreciate that the Rh third and fourth leadsadvantageously provide separation between the pinned portion of the biaslayers 1006, 1008 and the active portion of the sensor. A Ta cap 1042may be provided over the active portion of the sensor to protect thesensor from corrosion.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A magnetoresistive sensor, comprising: a ferromagnetic pinned layer; a ferromagnetic free layer, including first and second ferromagnetic layers separated by a non-magnetic antiparallel coupling layer, said first and second ferromagnetic layers having magnetizations antiparallel to one another in the absence of a magnetic field and free to rotate in the presence of a magnetic field; a non-magnetic spacer layer formed between said ferromagnetic free layer and said ferromagnetic pinned layer; first and second leads formed above said free layer, said leads having inner terminations defining a track width and extending outward from said track width; said pinned layer extending beyond said track width and terminating at first and second lateral sides; a first layer of antiferromagnetic material having an inner end abutting said first lateral side of said pinned layer and extending laterally outward there from, said layer of antiferromagnetic material contacting a portion of said free layer outside of said track width; and a second layer of antiferromagnetic material having an inner end abutting said second lateral side of said pinned layer and extending laterally outward therefrom, said second layer of antiferromagnetic material contacting a portion of said free magnetic layer.
 2. A magnetoresistive sensor as in claim 1 wherein; said free layer has a center portion disposed within said track width; said free layer has first and second outer portions beginning at first and second locations laterally disposed outside of said track width, and extending laterally outward therefrom; said free layer has first and second intermediate portions disposed between said inner portion and said outer portions; and said first and second layers of antiferromagnetic material are exchanged coupled with said second layer of said free layer in said first and second outer portions.
 3. A magnetoresistive sensor as in claim 2, wherein said first and second layers of antiferromagnetic material are exchange coupled with said free layer from first and second locations substantially coincident with said first and second locations of said beginning of said first and second outer portions.
 4. A magnetoresistive sensor as in claimed 2, wherein said first and second outer portions begin at first and second locations spaced from said center portion a distance of at least one half said track width.
 5. A magnetoresistive sensor as in claim 2 wherein at least one of said first and second layers of said free layer comprises refill material in said intermediate and outer portions.
 6. A magnetoresistive sensor as in claim 2, wherein said second layer of said free layer has a thickness in said intermediate and outer portions that is at least 15 percent thicker than a thickness of said second layer of said free layer in said center portion.
 7. A magnetoresistive sensor as in claim 2, wherein said second layer of said free layer has a thickness in said intermediate and outer portions that is at about 20 percent greater than a thickness of said second layer of said free layer in said center portion. 